This application claims the benefit of Korean Patent Application No. 2001-32194 filed with the Korea Industrial Property Office on Jun. 8, 2001, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a cathode ray tube (CRT), and more particularly, to a beam-index-type CRT that can optimize light reception efficiency of index light generated on a screen.
2. Description of the Related Art
Generally, a color CRT is designed to realize an image by electron-beams emitted from an electron gun and scanning a phosphor screen deposited with red R, green G, and blue B phosphors. As the CRT is not costly and provides a clear image, it is widely used as a TV and a computer monitor.
However, such a CRT is composed of a large number of parts, such as a color selection apparatus to select red R, green G, and blue B electron beams corresponding to the R, G, and B phosphors, and an inner shield to shield the electron beams from outer magnetic fields such as geomagnetism. In addition, when a shadow mask of the color selection apparatus is thermally expanded by electron beams within a high current range, the color purity of the CRT is deteriorated.
Therefore, in recent years, a beam-index-type CRT that does not use the shadow mask and the inner shield has been proposed. That is, the beam-index-type CRT has a phosphor screen on which index stripes for color selection are formed and an index light detector is mounted on a funnel. When a ray of the electron beam emitted from an electron gun excites a corresponding index stripe to generate the index light, the index light detector detects the index light to synchronize an index signal with a color signal, thereby realizing the desired color.
As the shadow mask is not used, electron beam mis-landing, caused by doming of the shadow mask, is prevented. In addition, as only a single electron beam ray is used to realize the color image, mis-convergence caused by a plurality of electron beams can be also prevented.
However, the phosphor should be precisely designed in its size so that the electron beam does not strike an undesired phosphor when a ray of an electron beam strikes a pixel of the phosphor, and the landing angle of the electron beam to a periphery of the screen should not be inclined.
In addition, as the location of the electron beam is controlled under the index signal, the definition of the image, the index light generated in the index stripe, should be effectively detected. That is, the light reception rate should be high. The light reception rate is highly affected by where the index light detector is mounted on the funnel.
More specifically, when the index light detector is mounted in the vicinity of the neck, although the index light generated in the index stripe provided on the center of the phosphor screen is effectively detected, the index light generated in the index stripe provided on the periphery of the phosphor screen is not effectively detected as the distance from the detector to the index stripe is far and the phosphors in the periphery area are close to the range out of the viewing angle of the detectors.
On the contrary, when the index light detector is mounted in the vicinity of a corner of the funnel, although the index light generated in the index stripe provided on the periphery of the phosphor screen is effectively detected, the index light generated in the index stripe provided on the center of the phosphor screen is not effectively detected as the distance from the detector to the index stripe is far and the phosphors in the periphery area are close to the range out of the viewing angle of the detectors.
For the above-described reason, Japanese Laid-open patent Nos. Sho 52-87356 disclose a beam-index-type CRT in which even numbers of index light detectors are mounted on the funnel symmetrically centering around a tube axis, and Sho 62-216138 disclose a beam-index-type CRT in which plural index light detectors are mounted on the funnel.
However, even though plural index light detectors are mounted on the funnel, mounting locations of the detectors to more effectively detect the index light generated on the index stripes provided on both the center and periphery of the phosphor screen are not accurately proposed.
Accordingly, it is an object of the present invention to provide a beam-index-type cathode ray tube (CRT) that can optimize the light reception rate of the index light generated on the center and periphery of the phosphor screen.
The foregoing and other objects of the present invention may be achieved by providing a beam-index-type CRT comprising a vacuum tube defined by a panel and a funnel having a neck; a phosphor screen provided with index stripes to provide color selection, the phosphor screen being formed on an inner surface of the panel; an electron gun mounted inside the neck to emit electron beams toward the phosphor screen; a deflection yoke mounted around the neck; a transparent light reception window provided on the funnel; a detector to generate an index signal by condensing index light generated from the index stripes through the light reception window; and an index circuit to transmit a signal obtained by synchronizing the index signal with a color signal, wherein when a diagonal length on the outer surface of the funnel is xe2x80x9cdxe2x80x9d, the center of the transparent light reception window is provided at a location within a range of 0.1-0.3 d along the outer surface of the funnel from a corner of a seal edge of the funnel.
In an embodiment of the present invention, the light reception window is provided on each of four connecting lines that respectively connect corners of a seal edge of the funnel to the neck.
Further, an embodiment of the present invention provides that the light reception window is provided at a location within a range defined by rotating the connecting lines by 0-30xc2x0 clockwise or counterclockwise.
The foregoing and other objects of the present invention may also be achieved by providing a beam-index-type CRT comprising a vacuum tube defined by a panel and plural funnels each having a neck; a phosphor screen provided with index stripes to provide color selection, the phosphor screen being formed on an inner surface of the panel; an electron gun mounted inside each of the necks to emit electron beams to the phosphor screen; a deflection yoke mounted around each of the necks; a transparent light reception window provided on each of the funnels; a detector to generate an index signal by condensing index light generated from the index stripes through the light reception windows; and an index circuit to transmit a signal obtained by synchronizing the index signal with a color signal, wherein when a diagonal length on the outer surface of each of the funnels is xe2x80x9cdxe2x80x9d, each center point of the light reception windows is provided on a location within a range of 0.1-0.3 d from a corner of a seal edge of each funnel.
In this embodiment, the phosphor screen is divided into at least two regions, and plural funnels corresponding to the divided regions are provided.